Recent advances in analytical techniques have enabled various biogenic components to be assayed. Particularly, in the clinical test field, various biogenic components in body fluids related to pathological conditions have been assayed with the development of immunoassay based on the principle of specific reaction between antigens and antibodies. In the field of such immunoassay, the point-of-care testing (hereinafter, also referred to as POCT) field has received attention in recent years on the grounds that: a time required from sampling to obtainment of test results can be shortened; an apparatus is convenient; and simple assay can be achieved.
Most of test instruments used in such immunoassay involve BF separation.
An immunochromatography test instrument is known as such a test instrument (Patent Literature 1). In this test instrument used, first antibodies against an analyte that may be present in a sample solution are immobilized, for example, on a sheet as a chromatography medium made of a porous material through which a liquid can be moved by capillarity. The sample solution containing labeled second antibodies, for example, gold colloid-labeled second antibodies, against the analyte is developed from the end of the chromatography medium in the test instrument. Subsequently, a complex of the first antibody, the analyte and the labeled second antibody is captured by the immobilized first antibody site. Since unreacted labeled antibodies are moved to downstream, color derived from the gold colloid or the like is observed at the immobilized antibody site only when the analyte is present in the sample. In the first place, this method merely determines the presence or absence of the analyte by the visual observation of the presence or absence of color derived from the gold colloid or the like and is disadvantageously incapable of quantitative assay.
Alternatively, a test instrument for analyte quantification is also known, in which a sample is transported via a spatial channel by pump suction (Patent Literature 2). This instrument comprises a sample supply port, a sample treatment chamber provided with labeled antibodies, an assay chamber provided with immobilized antibodies, a waste liquid chamber and a pump connecting port, wherein these members are communicated with each other via channels. A sample is applied to the sample supply port and transported by suction to the sample treatment chamber in which the labeled antibodies are in turn liberated and reacted with the analyte in the sample. Subsequently, the sample is transported by suction again to the assay chamber in which a conjugate of the immobilized antibody, the analyte and the labeled antibody is in turn formed and stopped for a given time. Components other than the analyte in the sample are transported into the waste liquid chamber by suction. Then, the analyte contained in the sample can be assayed quantitatively by the photometry of the analyte-derived conjugate located in the assay chamber. This instrument, however, is relatively difficult to control due to several stages of sample transport using a pump, and the assay results are disadvantageously largely influenced by conditions.
A method for solving these problems is also known, in which a channel-openable/closable occlusion member is combined with pump pressurization under the similar assay principle (Patent Literature 3). This method, however, requires the undesirably complicated structure of a test instrument.
Meanwhile, development examples of test instruments capable of quantifying an analyte through latex immunoagglutination reaction without the need of BF separation are also known, although few in number in the POCT field (Patent Literature 4). This method involves incorporating antibody-sensitized latex or the like in a dry state to a test instrument. In such a case, a liquid reagent must be produced in advance by time-consuming complicated freeze drying, not by simple natural drying. In the first place, antibody-sensitized particles are not completely dissolved in water but are merely dispersed therein. Thus, this method has the disadvantage that the dried antibody-sensitized particles are hardly redispersed. Unlike the method involving BF separation, the method based on the latex immunoagglutination reaction requires completely redispersing antibody-sensitized particles. Therefore, in the case of using latex immunoagglutination assay in dry chemistry, immunoassay must be performed by the application of spatial processing means such as rotation or shaking for latex redispersion. As a result, a test instrument used therein disadvantageously tends to be complicated.